The present invention relates generally to methods and apparatus for treating or controlling movement disorders by application of modulating electrical signals to a selected nerve or nerve bundle of the patient, and more particularly to techniques for treating patients with movement disorders by application of such signals to the vagus nerve or other suitable cranial nerve, using an implantable neurostimulator.
It is an object of the present invention to apply the techniques of selective modulation of vagus nerve electrical activity to the treatment of movement disorders, using a neurostimulator device which may be implantable, or used external to the body with only a small portion of the circuitry implanted or with only the nerve electrode(s) and associated lead(s) implanted percutaneously in the body.
In U.S. Pat. Nos. 4,702,254, 4,867,164 and 5,025,807, J. Zabara discloses methods and devices for treating and controlling epileptic seizures and certain motor disorders by selective stimulation of the vagus nerve. The disorders include involuntary movements of the patient during an epileptic seizure, or attributable to Parkinson""s disease, palsy or spastic disorders, for example. In the disclosure of the patents, the stimulating electrical pulse signal is preferably applied to the nerve in the patient""s neck region. In the ""734 patent, movement disorders are also mentioned in connection with discussion of the trigeminal and glossopharngyeal nerves.
In the ""254 patent, for example, Zabara discloses methods and devices for performing extra-physiologic electrical stimulation of the vagus nerve for treatment of epilepsy and various forms of involuntary movement disorders. An implantable pulse generator uses neurocybernetic spectral discrimination, in which the external current of the generator is tuned to the electrochemical properties of certain inhibitory nerves that affect the reticular system of the brain. These nerves are embedded within a bundle of other nerves, and are selectively activated directly or indirectly by the tuning of the generator to augment states of brain neural discharge to control convulsions or seizures. The generator may be activated manually by the patient upon recognizing a characteristic of the disorder, such as the classic aura at onset of a seizure, or automatically such as by sensor detection of instantaneous changes in certain state parameters at onset, for treatment only for the duration of the seizure. Alternatively, the generator may be activated for periodic prophylactic treatment.
It is a principal aim of the present invention to provide a new technique for treating movement disorders using stimulation of a suitable cranial nerve, particularly the vagus nerve.
The basic stimulation strategy of the present invention may be implemented by circadian programming to automatically activate the stimulus generator to continuously, periodically or intermittently generate an electrical signal appropriate for application to the patient""s vagus nerve to modulate its activity. In another aspect, the treatment is carried out by applying the selectively modulating electrical signals to the patient""s vagus nerve in response to the occurrence of a predetermined detectable event.
According to the present invention, a method of treating patients suffering from involuntary movement disorders, such as but not limited to epileptic seizures, Parkinson""s disease, palsy or spastic disorders, comprises unilateral or bilateral stimulation of the left and right vagi in the immediate vicinity of the patient""s diaphragm. The treatment is administered at either a supra-diaphragmatic position (i.e., above the diaphragm) or sub-diaphragmatic position (i.e., below the diaphragm) in the ventral cavity. The stimulating electrical signal is preferably applied to the vagus two to three inches above or below the diaphragm, and may be applied either synchronously or asynchronously to both the right and left branches, preferably in the form of a series of pulses applied intermittently to both branches according to a predetermined on/off duty cycle. The intermittent application is preferably chronic, rather than acute. However, continuous application or acute application by bilateral stimulation of the right and left vagi or unilateral stimulation of either branch of the nerve is also contemplated. Automatic delivery of bilateral intermittent stimulation is preferred, but alternatively in the case of certain movement disorders application of the stimulating electrical signal to the right and left vagi may be controlled by an external commencement signal produced by the patient""s placement of an external magnet or other signal generating mechanism in proximity to the location of the implanted device.
Preferably, the same stimulating electrical signal is applied to both the right and left vagi, but as an alternative, a stimulating electrical signal might be applied to the right vagus which is different from the stimulating electrical signal applied to the left vagus. And although two separate nerve stimulator generators may be implanted for stimulating the left and right vagi, respectively, as an alternative a single nerve stimulator generator may be implanted for bilateral stimulation if the same signal is to be applied to both the left and right branches of the vagus nerve, whether delivered synchronously or asynchronously to the vagi.
Preferably, the current magnitude of the stimulating signal is programmed to be less than about 6 mA, to be below the retching level of the patient as determined by the implanting physician at the time the implant procedure is performed. This is desirable to avoid patient nausea during periods of vagus nerve stimulation. Preferably, the pulse width is set to a value not exceeding about 500 microseconds (xcexcs), the pulse repetition frequency is set at about 20-30 Hertz (Hz), the VNS regimen follows alternating periods of stimulation and no stimulation, with the second period about 1.8 to 6 times the length of the first period in the alternating sequence (i.e., the on/off duty cycle is 1:1.8 to 1:6).
Alternative techniques include indirect stimulation of the vagus, either bilaterally or unilaterally, at a location near one or both branches of the nerve or elsewhere, which has the effect of stimulating the vagus nerve as well. This may be accomplished through afferents or efferents, for example. It is also contemplated that direct or indirect unilateral or bilateral stimulation, applied in the vicinity of the patient""s diaphragm, of one or more of the other cranial nerves of suitable sensory, motor or mixed fiber types may be effective in treating movement disorders, as an alternative to vagus nerve stimulation.
Some differences may be observed from stimulator to stimulator in magnitude of current in the pulses of the stimulation signal, and may be attributable to things such as patient impedance, variation of the vagus nerve from right to left or between patients, and variation in contact between the vagus and the electrode implanted thereon from implant to implant.